I'd cut a large piece of cardboard as a backer and put several 4" target dots on it far enough apart that there'll be no confusion between shots and do 3 to five shots on a dot, using a different dot with each change. You can do the basic shooting using different charges, bullets, ect at 50 yards. At 50 yards, differences will be very apparent. One you've found a charge and bullet/sabot that you can live with, run a target out to 100 and do your fine tuning at that distance.
Remember that while you're doing all this shooting, you'll want to shoot slow enough to keep the barrel relatively cool and you'll also want to pull the breech plug after every 15 or so shots the ream the flash channel behind the primer pocket since too much build-up of carbon in there can sway your shooting results. If you're shooting say ten different loads/bullets five times each, you'll be looking at maybe four to five hours of range time, so maybe spread the shooting of these different charges and bullets between a couple different sessions so YOU are not getting shot out. Recoil can get old too and come into play as well. And like doing anything, not all days are going to be good ones so if you catch yourself flinching or practicing some other little bad habit maybe consider just packing it in for the day.... no sense in practicing something that is getting in the way of some meaningful shooting.